For the last few years both domestic and foreign automobile manufacturers have been using heat bondable sheet sound deadeners which are placed in the car body prior to the final paint oven. In the oven the sound deadener sheet softens, conforms to the contours of the body and bonds without excessive sag or flow from the sloped or vertical areas. This type of material is also being used in areas where high inservice temperatures (190-400.degree. F.) would result in flowing of standard asphaltic deadeners.
The majority of the heat bondable sound deadener sheets used domestically contain asbestos to control the melt flow properties of the asphalt at elevated temperatures, however, asbestos being a known carcinogen requires special handling thereby complicating the manufacture of the product.
A typical asbestos-containing formula would be:
5% 7R Asbestos PA1 67% Ground Limestone Filler PA1 28% Asphalt
Other heat bondable sound deadeners which are available are based on thermoplastic resins such as butadiene-styrene, coumarone-indene, styrene-indene, such as disclosed in British Pat. No. 1,039,711 and Canadian Pat. Nos. 721.237 and 784.029. These compositions, however, tend to be more expensive and more difficult to manufacture than the asbestos-containing sound deadening material.
The main object of the invention is to provide a heat bondable sound deadener sheet which is asbestos-free, inexpensive and can be manufactured using the same equipment as the present asbestos compositions.